Memory element and memory device

ABSTRACT

A memory element wherein a spin conduction layer having a sufficient spin coherence length and a uniform spin field can be obtained, and thereby practical use is attained and a memory device are provided. A spin conduction layer (paramagnetic layer) ( 24 ) is a fullerene thin film being from 0.5 nm to 5 μm thick, for example. The fullerene has a hollow sized, for example, from 0.1 nm to 50 nm. A paramagnetic material is included in this hollow. A fermi vector of the fullerene thin film well laps over small number of spin band or plenty of spin band of a ferromagnetic fixed layer ( 23 ) and a ferromagnetic free layer ( 25 ). Further, spin orientations of the included paramagnetic material are random. Further, electron spin in the fullerene is in a quantized state in a pseudo zero dimensional space. Thereby, a spin coherence length becomes long in the fullerene thin film, and scatteration of spin-polarized conduction electrons goes away.

TECHNICAL FIELD

The present invention relates to a memory element for writing recordinginformation by injecting spin-polarized electrons and a memory deviceusing this memory element.

BACKGROUND ART

Under the circumstances that the high speed network society has come, inthe mobile media rapidly becoming popular such as mobile phones andlaptop computers, development of nonvolatile memories has beenparticularly required. The nonvolatile memory can retain data withoutbeing always supplied with electric power. Therefore, in the devicesusing the nonvolatile memory can be run immediately after the power isturned on. Further, power consumption can be reduced.

A Magnetic Random Access Memory (MRAM) recently noted comprises highspeed characteristics of a SRAM (Static RAM), high density and lowercost characteristics of a DRAM (Dynamic RAM), and nonvolatilecharacteristics of a flash memory. Therefore, the MRAM is considered asa promising memory of a future de facto standard. The MRAM is a memoryusing magnetic effects. Of the MRAM, a spin valve type memory utilizinggiant magnetoresistive effects, and a memory utilizing spin dependenttype tunneling effects are known. In these MRAMs, a switching current isapplied to a wiring corresponding to a targeted memory cell and amagnetic field is generated, by which a magnetization state of arecording layer in the cell is changed and bit information is written.Information is read by detecting a magnetization state of the cell byutilizing magnetic effects. As above, the MRAM is a solid-state memory.Therefore, there is no risk of damage, which might occur in a magneticrecording medium for performing writing and reading mechanically byusing a magnetic head. The MRAM also excels at repeating writing andreading.

However, for practical use of the MRAM, problems caused along with highdensity of memories have been left. A magnetic strength required forwriting is in inverse proportion to a width of a recording layer, thatis, a cell size. Therefore, when a memory cell is miniaturized, aconsumption power becomes very large. Further, there is a risk thatcross talk may be caused by a proximate leakage magnetic field betweenadjacent cells. For example, for a memory cell being 0.2 μm wide, acurrent in writing becomes several mA. Further, for a memory whose celldistance narrows down to about 0.1 μm, when a magnetic field is inducedfor a targeted cell, a magnetic field having 80% intensity thereof isapplied to its adjacent cell.

As a technique to solve the foregoing problems, a MRAM using a newwriting method called polarized spin injection method to a recordinglayer has been suggested (refer to Japanese Unexamined PatentApplication Publication No. H11-120758). This memory element isconstructed as in FIG. 22. That is, a ferromagnetic layer (fixed layer)111 wherein a magnetization direction is always fixed and aferromagnetic layer (free layer) 112 wherein a magnetization directionis changed according to bit information are separated by a paramagneticlayer 113. Paramagnetic metal layers 114 and 115 are electrode layersfor applying a current in the laminating direction to the ferromagneticlayers 111 and 112. In the polarized spin injection method, polarizedelectrons are injected into the ferromagnetic layers 111 and 112 and aspin angular momentum is conveyed by applying a spin polarized currentin the laminating direction. Thereby, in the ferromagnetic layer 112, amagnetic moment is inverted by interaction. This mechanism is calledspin conversion. In the writing method wherein magnetization is switchedby injecting a spin current as above, there is no need to apply anexternal magnetic field. Therefore, it is free from interference betweenmemory cells, and power consumption can be restrained. The polarizedspin injection method is further characterized in that its writing timedepends on only a spin conduction rate. Therefore, a response rate canbe improved.

However, in this technique, there has been also a problem for practicaluse. The paramagnetic layer 113 arranged between the ferromagneticlayers 111 and 112 has an aspect as a spin conduction layer forconducting the polarized spin of electrons without relaxation, inaddition to a role as a magnetic spacer. Therefore, it is necessary thatthe paramagnetic layer 113 is made of a material having a long spincoherence length and having a very small spin scatteration to theferromagnetic layers 111 and 112.

That is, when a spin orientation is changed by, for example,scatteration of spin-polarized conduction electrons in the paramagneticlayer 113, spin information of the conduction electrons have becomeslost. Therefore, the paramagnetic material having a long spin coherencelength is desired. To date, researches on spin conduction of theparamagnetic layer have been conducted by using a paramagnetic metalmaterial, a semiconductor material and the like.

However, when the foregoing material is used for the paramagnetic layer,it is difficult to grow a uniform thin film, and to control the spincoherence length. Therefore, there has been a problem that a sufficientspin coherence length and a uniform spin field cannot be obtained in theparamagnetic layer. In the result, regarding the memory element of thespin injection method, though it is theoretically shown that significanteffects can be obtained compared to the conventional induced magneticfield method, sufficient characteristics have not been obtainedpractically. Therefore, its practical use has not been attained.

In view of the foregoing, it is an object of the invention to provide amemory element capable of obtaining a sufficient spin coherence lengthand a uniform spin field in the paramagnetic layer, and therebyattaining practical use thereof, and a memory device using it.

DISCLOSURE OF THE INVENTION

A memory element according to the invention is a memory element whereinrecording information is written by injecting spin-polarized electronscomprising: a spin conduction layer made of a spherical shell orcylindrical molecule material having a hollow, and wherein thespin-polarized electrons are conducted by the spin conduction layer.

More specifically, the memory element of the invention is a memoryelement primarily comprising: a first ferromagnetic layer wherein amagnetization direction is fixed; a spin conduction layer made of aspherical shell molecule material having a hollow in which aparamagnetic material is included and having a given spin coherencelength, which is formed over the first ferromagnetic layer; and a secondferromagnetic layer formed on the spin conduction layer on the sideopposite to the first ferromagnetic layer, wherein a magnetizationdirection is changed by the spin-polarized electrons, wherein therecording information is written by changing the magnetization directionof the second ferromagnetic layer.

In this memory element, when the spin-polarized electrons are injectedinto the second ferromagnetic layer, the magnetization direction of thesecond ferromagnetic layer is changed, and the recoding information iswritten. Then, a spin-polarized electron flow flows without spinscattering through the paramagnetic layer made of the spherical moleculematerial including the paramagnetic material (for example, carbonmolecule fullerene) which has a sufficient spin coherence length and auniform spin field. That is, the injected electrons are conductedthrough the paramagnetic layer while their spin polarization degree ismaintained.

Secondly, a memory element of the invention is a memory elementcomprising: first and second ferromagnetic layers wherein amagnetization direction change of at least one thereof is induced byinjecting the spin-polarized electrons; and a spin conduction layerconstructed from at least part of a hollow cylindrical molecule (forexample, carbon nanotube) arranged by setting its axis direction to alaminating direction of the first and the second ferromagnetic layers,which is provided between the first ferromagnetic layer and the secondferromagnetic layer to shield magnetic interaction thereof and whichconducts the spin-polarized electrons.

In the memory device, a current flows in the axis direction of thehollow cylindrical molecule functioning as the spin conduction layer.Thereby, the spin-polarized electrons are conducted between the firstferromagnetic layer and the second ferromagnetic layer. In the spinconduction layer, electrons are conducted without spin relaxationaccording to a spin coherence length of the cylindrical molecule or asubstance included in a hollow part thereof, and an angle momentumthereof is given to the first ferromagnetic layer and the secondferromagnetic layer.

The memory device of the invention is constructed by arraying aplurality of memory elements of the invention described above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a pattern diagram showing an outline construction of a memoryelement according to a first embodiment of the invention;

FIG. 2 is a pattern diagram of a memory cell;

FIG. 3 is a view for explaining a crystal structure of a fullerene thinfilm used for a spin conduction layer (paramagnetic layer);

FIGS. 4A to 4C are pattern diagrams for explaining an operation ofwriting into the memory cell;

FIGS. 5A to 5C are also pattern diagrams for explaining the operation ofwriting;

FIGS. 6A and 6B are pattern diagrams showing a reading signal to thememory cell;

FIGS. 7A and 7B are also pattern diagrams showing the reading signal;

FIG. 8 is a view for explaining an addressing scheme of the memory cell;

FIG. 9 is also a view for explaining the addressing scheme;

FIG. 10 is a plan view for explaining a step of manufacturing the memoryelement shown in FIG. 1;

FIGS. 11A to 11C are cross sections of steps following FIG. 10;

FIG. 12 is a cross section of a step following FIG. 11C;

FIG. 13 is a plan view of FIG. 12;

FIGS. 14A to 14C are cross sections of steps following FIG. 12;

FIGS. 15A to 15C are cross sections of steps following FIG. 14C;

FIG. 16 is a plan view of FIG. 15C;

FIG. 17 is a view showing a modification of the memory cell;

FIG. 18 is a view showing another modification of the memory cell;

FIG. 19 is a view showing a construction of a memory element accordingto a second embodiment of the invention;

FIG. 20 is an outline construction view of a memory device constructedby integrating the memory elements shown in FIG. 19;

FIG. 21 is a view showing a modification of the memory element; and

FIG. 22 is a construction view of a conventional spin injection typememory element.

BEST MODES FOR CARRYING OUT THE INVENTION First Embodiment

FIG. 1 shows a construction of a memory element according to a firstembodiment of the invention. The memory element MM1 is a “spin injectiontype” element for performing writing by causing magnetization inversionby injecting polarized spin electrons. FIG. 2 shows a taken out memorycell 20 constructing the memory element MM1.

The memory element MM1 is a memory element wherein a plurality of memorycells 20 are arrayed in a state of a matrix (for example, array of Mcolumns and N lines: M×N array). Recording information of the memorycell 20 is written by injecting a spin-polarized electron flow into eachmemory cell 20 (spin injection method). It is preferable that anin-plane size of this memory cell 20 is from 0.5 nm² to 5 μm². When thesize of the memory cell is small, cross talk may be caused. It becomespossible to inhibit influence of a magnetic field due to a writingcurrent to the adjacent respective memory cells 20 each other by settingto the foregoing size.

The memory cell 20 comprises a substrate 21. An electrode layer 22 isformed on the substrate 21. A ferromagnetic fixed layer (firstferromagnetic layer) 23 made of a ferromagnetic material is formed onthe electrode layer 22. In the ferromagnetic fixed layer 32, amagnetization direction is fixed in a given direction. A spin conductionlayer 24 is formed on the ferromagnetic fixed layer 23. In thisembodiment, the spin conduction layer 24 is made of a spherical shellmolecule material including a paramagnetic material, for example, carbonmolecule fullerene. Detailed description thereof will be given later. Aferromagnetic free layer (second ferromagnetic layer) 25 made of aferromagnetic material is formed on the spin conduction layer 24. Theferromagnetic free layer 25 has two stable magnetization directions, andis oriented to one of two magnetization directions. The magnetizationdirection of the ferromagnetic free layer 25 is changed according tospin of conduction electrons. An electrode layer 26 is formed on theferromagnetic free layer 25.

The substrate 21 is, for example, made of silicon (Si). The electrodelayers 22 and 26 are made of a paramagnetic metal such as gold (Au). Asthe paramagnetic metal, any material other than gold can be used as longas a wiring can be easily fabricated with such a material to theelectrode layers 22 and 26 by deposition method, sputtering method andthe like.

The spin conduction layer 24 is a fullerene thin film made of afullerene 24 a including a paramagnetic material 24 b as mentionedabove. A thickness thereof is, for example, from 0.5 nm to 5 μm. Such afullerene thin film has a crystal structure as shown in FIG. 3. Thefullerene thin film generally has a crystal structure of fcc. However,in this figure, it is expressed by a two dimensional simple lattice forconvenience.

The fullerene 24 a has a hollow sized, for example, from 0.1 nm to 50nm. In this hollow part, the paramagnetic material 24 b is included.Examples of the fullerene 24 a include C₃₆, C₆₀, C₇₀, C₇₂, C₇₄, C₇₆, andC₈₂. Examples of the paramagnetic material 24 b include rare earthelements such as lanthanum (La), cesium (Cs), dysprosium (Dy), europium(Eu), and gadolinium (Gd); and nonmetallic elements such as N (nitride)and P (phosphorus).

Further, in the fullerene thin film, spin orientations of the includedparamagnetic material 24 b are random. Therefore, the fullerene thinfilm has stable paramagnetism. Further, electron spin in the fullerene24 a is in a quantized state in a pseudo zero dimensional space.Therefore, in the fullerene thin film, spin relaxation time becomeslong, that is, a spin coherence length becomes long. In the result, whenelectrons are conducted through the fullerene 24 a, spin is neverscattered. For example, when electrons are conducted in the verticaldirection as shown in the figure, the electrons can be conducted while aspin polarization degree is maintained.

In this embodiment, as shown in FIG. 2, the magnetization direction ofthe ferromagnetic fixed layer 23 is fixed in a magnetization directionS₁. Meanwhile, the magnetization direction of the ferromagnetic freelayer 25 is one of two stable magnetization directions S₁ and S₂, forexample, S₂. In the ferromagnetic free layer 25, when the spin-polarizedelectron flow is injected, the magnetization direction is rotated. Twomagnetization directions of the ferromagnetic free layer 25 correspondto two types of recording information in the memory cell 20. These twotypes of recording information are read as signals, “1” and “0.” In FIG.2, the magnetization directions S₁ and S₂ are depicted as orthogonalcoordinate axes.

In this embodiment, the following ferromagnetic materials areselectively used so that the ferromagnetic fixed layer 23 and theferromagnetic free layer 25 have functions different from each other.

Simple Substance: (110) orientation bcc Fe (001) orientation bcc Fe Caxis in-plane orientation hcp Co (111) orientation fcc Co (110)orientation fcc Co (001) orientation fcc Co

Binary Alloy:

Fe_(1-r)Co_(x) (0<x<1)

Ni_(x)Fe_(1-x) (0<x<0.75)

Ni₇₉Fe_(2l) (permalloy)

Tertiary Alloy:

MnFeCo

FeCoNi

Here, selection of the foregoing ferromagnetic materials is inaccordance with the following conditions. For example, when the sameferromagnetic material is used for the ferromagnetic fixed layer 23 andthe ferromagnetic free layer 25, the ferromagnetic fixed layer 23 isformed thicker than the ferromagnetic free layer 25. When the materialfor the ferromagnetic fixed layer 23 is different from the material forthe ferromagnetic free layer 25, selection is made so that the materialfor the ferromagnetic fixed layer 23 has a very larger gilbertattenuation coefficient compared to that of the material for theferromagnetic free layer 25.

Further, when the materials for each layer of the ferromagnetic fixedlayer 23 and the ferromagnetic free layer 25 have current polarizationefficiencies different from each other, it becomes possible that writingcurrents and writing times required in writing from recordinginformation “0” to “1” or from “1 to “0” can be values different fromeach other. Providing the writing current with asymmetry postulate isadvantageous in constructing a circuit, for example, a polarity capableof reducing a current required per cell can be selected when all memorycells 20 on the chip are concurrently cleared.

Further, as mentioned above, since the ferromagnetic free layer 25 hastwo stable magnetization directions, it is important that theferromagnetic free layer 25 has uniaxial anisotropy in the layer. Thatis, the ferromagnetic free layer 25 needs to have magnetic field Hu withuniaxial anisotropy larger than 100 Oe (oersted), which is free frominfluence of heat or fluctuation of magnetic field. Further, uniaxialanisotropy of the ferromagnetic fixed layer 23 have to be larger thanthat of the ferromagnetic free layer 25. When a ferromagnetic materialhaving magnetic field Hu with small uniaxial anisotropy is used for theferromagnetic free layer 25, it is easy to switch the magnetizationdirection between S₁ and S₂. However, CCP voltage measurement for thissystem requires subtle experimental conditions. That is, a memory cellfabricated from a material having magnetic field Hu with too smalluniaxial anisotropy is not suitable as a practical device. Such uniaxialanisotropy can be obtained by controlling composition, shape, crystalorientation, and lattice strain of the ferromagnetic material, or bycontrolling a magnetic field applied in forming these layers. Morespecifically, as a ferromagnetic thin film having uniaxial anisotropy,the following can be cited.

For example, the (110) face bcc iron which is magnetized alongmagnetizable axis direction determined by magnetic anisotropy(<001>direction) has magnetic field Hu with a high polarization ratioand high uniaxial anisotropy. Further, for example, the permalloy whichis deposited under the existence of a bias magnetic field and providedwith uniaxial induced magnetic anisotropy parallel to the magnetic fieldhas magnetic field Hu with optimal polarization efficiency and smalluniaxial anisotropy. Further, for example, the hcp cobalt comprisinguniaxial anisotropy in the direction of in-plane c axis has magneticfield Hu with high polarization efficiency and high uniaxial anisotropy.In addition, the Fe_(1-x)Co_(x) alloy having bcc structure by, forexample, Co substitution by x% in Fe lattice site has its film face of(110), and has a magnetizable axis with in-plane uniaxial magneticanisotropy in the direction of <100>. The Fe_(1-x)Co_(x) alloy hasmagnetic field Hu with the largest polarization efficiency and largeuniaxial anisotropy.

Further, when a magnetization direction is changed in the plane of thelayer in the ferromagnetic free layer 25, it is possible to optimizeanisotropic magnetic field Hu by selecting a fineness ratio of arectangle shape whose short side is 1 μm or less. Meanwhile, when amagnetization direction is changed between the in-plane of theferromagnetic free layer 25 and the direction perpendicular to thein-plane, it is preferable that a thickness of the ferromagnetic freelayer 25 is 5 atomic layers or less in order to obtain sufficientvertical magnetic anisotropy. That is, it is preferable that thethickness of the ferromagnetic free layer 25 is about 1 nm. Thisthickness is a transition region between a case that the magnetizationdirection becomes in the in-plane direction and a case that themagnetization direction becomes perpendicular to the in-plane. Further,as a polarization electron source for the ferromagnetic fixed layer 23and the ferromagnetic free layer 25, a whistler alloy such as PtMnSb ora metalloid material can be used.

Next, operation of the memory element MM1 having such a constructionwill be hereinafter described. In this memory element MM1, amagnetization direction of the ferromagnetic fixed layer 23 is fixed toa given direction S₁. Meanwhile, the ferromagnetic free layer 25 has twostable magnetization directions S₁ and S₂, and is oriented to one ofthese magnetization directions (here, S₂). In such a memory element MM1,two magnetization directions of the ferromagnetic free layer 25correspond to two recording information in each memory cell 20.Recording information “1” or “0” is written by injecting aspin-polarized electron flow into the ferromagnetic free layer 25 andswitching the magnetization direction. Meanwhile, reading the recordinginformation is performed by utilizing giant magnetoresistive effects(GMR) generated by vertically applying a current in the memory cell 20.

When recording information is written, a pulse current is used in orderto switch the magnetization direction of the ferromagnetic free layer25, and magnetic switching (magnetic inversion) of the ferromagneticfree layer 25 is performed. For example, writing in the case that aninitial state is parallel magnetization alignment (FIG. 4A) is performedas follows. That is, electron particle density pulse Jp with spin in thesame direction as of the spin in the ferromagnetic free layer 25 flowsfrom the ferromagnetic free layer 25 to the ferromagnetic fixed layer23. Then, the ferromagnetic fixed layer 23 is exclusively in a state ofspin in the same direction as of the electron particle density pulse Jp.Therefore, spin of the electron particle density pulse Jp injected intothe ferromagnetic fixed layer 23 is inverted based on the Pauliexclusion principle. An electron flow having such inverted spin flows inthe direction opposite to of the electron particle density pulse Jp ascurrent density pulse Je (switching current I), and therefore, thedirection of the spin of the ferromagnetic free layer 25 is inverted. Asshown in FIG. 4B, the switching current I is larger than the criticalvalue Jt (A) in a joint region, and pulses are maintained in units ofnanosecond.

As described above, the magnetization direction of the ferromagneticfree layer 25 is inverted by the switching current I, the magnetizationdirection of the ferromagnetic free layer 25 becomes opposite to of theferromagnetic fixed layer 23, and it becomes in a state of anti-parallelmagnetization alignment (FIG. 4C). Thereby, writing is finished. The“parallel magnetization alignment” means that the magnetizationdirections of the ferromagnetic free layer 25 and the ferromagneticfixed layer 23 are the same. Further, the “anti-parallel magnetizationalignment” means that the magnetization directions of the ferromagneticfree layer 25 and the ferromagnetic fixed layer 23 are opposite.

Further, in the case that writing is performed when, for example, aninitial state is the anti-parallel magnetization alignment (FIG. 5A),respective flowing directions of the electron particle density pulse Jpand the current density pulse Je become opposite to each other. Theelectron particle density pulse Jp flows from the ferromagnetic fixedlayer 23 to the ferromagnetic free layer 25, and the electron densitypulse Je (switching current I) flows in the direction opposite to of theelectron particle density pulse Jp, and thereby writing is started. Thatis, the electron particle density pulse Jp with spin in the samedirection as of the spin in the ferromagnetic fixed layer 23 flows fromthe ferromagnetic fixed layer 23 to the ferromagnetic free layer 25.

Then, spin whose direction is different from of the spin in theferromagnetic free layer 23 is injected in the ferromagnetic free layer23. The spin of the ferromagnetic free layer 23 is torqued by thisinjected spin, and inverted. A current flow having this inverted spinflows in the direction opposite to of the electron particle densitypulse Jp as the current density pulse Je (switching current I). As shownin FIG. 5B, the switching current I is larger than the critical value Jt(A) in the joint region, and pulses are maintained in units ofnanosecond. As described above, the magnetization direction of theferromagnetic free layer 25 is inverted by the switching current I, themagnetization direction of the ferromagnetic free layer 25 becomes thesame as of the ferromagnetic fixed layer 23, and it becomes in a stateof parallel magnetization alignment (FIG. 5C). Thereby, writing isfinished.

Meanwhile, when recording information is read, for example, arrangementis set to CPP in which a current is vertically applied in the memorycell 20, and giant magnetoresistive effects are utilized. For example,in the case of the state of parallel magnetization alignment (FIG. 6A),when a reading current pulse of the critical value Jt or less isapplied, low voltage pulse V_(low) corresponding to logic “0” can beobtained (FIG. 6B). Further, for example, in the case of the state ofanti-parallel magnetization alignment (FIG. 7A), when a reading currentpulse of the critical value Jt or less is applied, high voltage pulseV_(high) corresponding to logic “1” can be obtained (FIG. 7B).

When such a reading method is adopted, in order to obtain, for example,5% or more of GMR ratio (ΔR/R), it is preferable that polarizations Pol₁and Pol₂ of electrons of materials constructing the respective layers,the ferromagnetic fixed layer 23 and the ferromagnetic free layer 25,satisfy the following Mathematical formula 1. $\begin{matrix}{\frac{2 \cdot {Pol}_{1} \cdot {Pol}_{2}}{1 - {{Pol}_{1} \cdot {Pol}_{2}}} > 0.3} & \left( {{Mathematical}\quad{formula}\quad 1} \right)\end{matrix}$

As an addressing scheme for such a memory element MM1, the simplestmethod is used. For example, as shown in FIG. 8, a method wherein onewrite only wiring 41 is used for one memory cell 20 can be cited.Further, for example, as shown in FIG. 9, so-called xy addressing schemewherein wirings 42 and 43 are provided so that the wirings 42 and 43cross, the memory cell 20 is arranged at the intersection of thesewirings 42 and 43, and addressing is made by combination of signals tothe wirings 42 and 43 can be cited.

In the case of the addressing scheme having the write only wiring 41,wire connection required for one memory cell 20 is made at one place inthe electrode layer 22 and two places in the electrode layer 26, andpseudo four terminal measurement is performed. In some cases, it isenough to perform two terminal measurement wherein wire connection ismade at one place respectively in the electrode layers 22 and 26.

In the case of the xy addressing scheme, only when a pulse isconcurrently applied to both the x and y wirings 43 and 44, a currentover the writing critical current is applied, and thereby, the memorycell 20 is selected. Then, it is possible that in order to assurecorrespondence of the pulse in the memory cell 20 wherein writing isperformed, a long pulse is given to one of the x wiring and y wiring(for example, x wiring), and a short pulse is given to the other wiring(y wiring).

Next, a method of manufacturing the foregoing memory element MM1 will behereinafter described with reference to FIGS. 10 to 16. FIG. 10 is aplan view of FIG. 11A; FIG. 13 is a plan view of FIG. 12; and FIG. 16 isa plan view of FIG. 15C.

First, as shown in FIGS. 10 and 11A, the substrate 21 made of, forexample, silicon is prepared. The substrate 21 is not provided withdoping, and, for example, is 4 inches in outer diameter and 0.01 inchesthick. Further, since a formation region of the electrode 22 is carvedout in a subsequent step, the substrate 21 is carved by a diamond point.After a surface of the substrate 21 is polished, the substrate 21 iswashed and provided with oxidation treatment. Next, the electrode layer22 made of, for example, Au is deposited in a region in theapproximately in-plane center of the substrate 21 (the size of 2 cm×2cm, for example), for example, by deposition method. A thickness of theelectrode layer 22 is set to, for example, 0.5 μm.

Next, as shown in FIG. 11B, a resist film 31 being 50 nm or more thickis formed on the electrode layer 22, for example, by photolithographymethod. Then, the resist film 31 is provided with patterning accordingto a shape of the memory cell 20.

Subsequently, as shown in FIG. 11C, the ferromagnetic fixed layer 23made of a permalloy having a composition of Ni₈₁Fe₁₉ is deposited by,for example, deposition method. A thickness of the ferromagnetic fixedlayer 23 is set to, for example, 4 nm. Further, when the ferromagneticfixed layer 23 is deposited, uniaxial anisotropy are induced while 100Oe of magnetic field is applied.

Next, the spin conduction layer 24 being 20 nm thick made of, forexample, C₈₂ including La (La@C₈₂) is deposited by, for example, plasmadeposition method. C₈₂ has a hollow sized, for example, from 0.1 nm to50 nm. La is included in this hollow. Then, the uniaxial anisotropy ofthe ferromagnetic fixed layer 23 is retained. More specifically, in theplasma deposition method, a plasma polymerization apparatus of, forexample, external electrode capacity combination type or parallel flatsheet electrode capacity combination type is used (for example, refer toJapanese Unexamined Patent Application Publication No. H08-59220). Thisplasma polymerization apparatus is provided with a molybdenum boatconnected to a plasma power source in a reaction vessel. C₈₂ powders arehoused in this molybdenum boat. The substrate 21 over which theferromagnetic fixed layer 23 is deposited is arranged in the positionfacing to the molybdenum boat in the reaction vessel.

By using such a plasma polymerization apparatus and setting the plasmapower source to, for example, AC 13.56 MHz, and an output to 150 W,positive ion plasma of La is generated in a constant flow system, C₈₂powders in the molybdenum boat are sublimated at several 100° C., andthe spin conduction layer 24 made of La@C₈₂ is deposited on theferromagnetic fixed layer 23 of the substrate 21. In this embodiment,the spin conduction layer 24 is deposited by the fullerene including theparamagnetic material (for example, La@C₈₂). Therefore, it is possibleto grow a uniform thin film, and control the spin coherence length.

Next, the ferromagnetic free layer 25, for example, being 1 nm thickmade of the permalloy is deposited on the spin conduction layer 24 by,for example, deposition method. Then, by performing deposition whileapplying a magnetic field similar to in depositing the ferromagneticfixed layer 23, uniaxial magnetic anisotropy are induced in theferromagnetic free layer 25, so that the c axis of the ferromagneticfree layer 25 becomes parallel to the magnetization of the ferromagneticfixed layer 23. Thereby the ferromagnetic free layer 25 has two stablemagnetization directions S₁ and S₂, and is oriented to one of thesemagnetization directions S₁ and S₂.

Subsequently, the electrode layer 26 being 25 nm thick made of, forexample, gold is deposited by deposition method. Next, as shown in FIGS.12 and 13, lift-off is performed by dissolving and removing the resistfilm 31. A memory cell part 32 a and an earth terminal part 32 b arethereby formed selectively.

Next, as shown in FIG. 14A, an insulating layer 33 made of polymethylmethacrylate being, for example, 60 nm thick is formed over thesubstrate 21 to cover the memory cell part 32 a and the earth terminalpart 32 b. The insulating layer 33 functions as a planarizing film.Next, as shown in FIG. 14B, top faces of the memory cell part 32 a andthe earth terminal part 32 b are exposed by, for example, oxygen plasmaetching method.

Subsequently, a resist film 34 is selectively formed as shown in FIG.14C. The resist film 34 has a pattern to cover the earth terminal part32 b and to expose the memory cell part 32 a. A thickness of the resistfilm 34 is set to, for example, 0.2 μm. Next, as shown in FIG. 15A, agold layer 35 made of, for example, Au is deposited to cover the resistfilm 34.

Subsequently, as shown in FIG. 15B, lift-off is performed by dissolvingand removing the resist film 34, and the gold layer 35 is selectivelyremoved. The gold layer 35 becomes one electric contact of the memorycell 20, and is electrically connected to the electrode layer 26. Whenthe resist film 34 is dissolved and removed, the earth terminal part 32b is exposed. However, the earth terminal part 32 b is electricallyconnected to the other electrode layer 22.

Next, as shown in FIG. 15C, wires for voltage signal 36 and 37 and wiresfor current pulses 38 and 39 are connected to these electric contacts(earth terminal part 32 b and gold layer 35) by bonding. Finally, thesubstrate 21 on which the memory cell 20 is formed is firmly fixed to aheat sink (not shown) made of copper (Cu). The memory element MM1 isthereby completed.

In the memory element MM1 constructed as above, two magnetizationdirections S₁ and S₂ of the ferromagnetic free layer 25 correspond totwo recording information in each memory cell 20. By injecting aspin-polarized current flow into this ferromagnetic free layer 25 andswitching the magnetization direction, writing “1” or “0” is performed.

Then, the spin-polarized electron flow flows through the spin conductionlayer 24. In this embodiment, the spin conduction layer 24 is made ofthe fullerene thin film (FIG. 3). In the fullerene thin film,orientations of spin of the included paramagnetic material 24 b arerandom. Therefore, the fullerene thin film has stable paramagneticcharacteristics. Further, electron spin in the fullerene 24 a is in aquantized state in a pseudo zero dimensional space. In addition, byconstructing the spin conduction layer 24 from the fullerene thin film,growing a uniform thin film and controlling the spin coherence lengthcan be easily performed. Thereby, in the spin conduction layer 24, asufficient spin coherence length and a uniform spin field can beobtained, and spin scattering can be prevented. That is, electrons areconducted through the spin conduction layer 24 while the spinpolarization degree thereof is maintained.

As described above, in this embodiment, the spin conduction layer 24 hasthe hollow sized from 0.1 nm to 50 nm, and is made of the fullereneincluding the paramagnetic material in the hollow. Therefore, it becomeseasy to grow a uniform thin film and control a spin coherence length,and a sufficient spin coherence length and a uniform spin field can beobtained. Therefore, it becomes possible to prevent scattering of thespin-polarized conduction electrons, and reliability is improved.Thereby, the spin injection type memory element MM1 can be put intopractical use. In particular, compared to the conventional inducedmagnetic field type, the upper limit of recoding density can be largelyimproved, and reading time and power consumption can be reduced.

The invention has been described with reference to the embodiment.However, the invention is not limited to the foregoing embodiment, andvarious modifications may be made. For example, it is possible that inorder to fix the magnetization direction of the ferromagnetic fixedlayer 23 to a given direction, a magnetization fixed layer 51 (refer toFIG. 17) made of, for example, anti-ferromagnetic material is formedover the ferromagnetic fixed layer 23. As an anti-ferromagneticmaterial, FeMn, IrMn, NiMn, RhMn, CrMnPt, FeMnpt and the like can becited. Of the foregoing, NiMn is suitable since NiMn can obtain a largepinning field even at high temperatures (for example, about 650 Oe up toT=450 K).

A magnetic moment of the ferromagnetic fixed layer 23 is pinned by sucha magnetization fixed layer 51, and its magnetization direction is fixedto a given magnetization direction. When the magnetization fixed layer51 is made of a metal as a anti-ferromagnetic material, themagnetization fixed layer 51 can also function as an electrode. Further,though the GMR effects are utilized for a method to read the recordinginformation in the foregoing embodiment, for example, magnetic Kerreffect generated when the ferromagnetic free layer 25 is illuminatedwith light can be utilized.

Further, as shown in FIG. 18, a spin arrayed layer 52 including a dilutemagnetic alloy can be provided in addition to the foregoing spinconduction layer 24. The dilute magnetic alloy is an alloy wherein amagnetic material metal is doped to a semiconductor. On a jointinterface between the dilute magnetic material, in which characteristicsof the semiconductor are maintained and magnetic order exists and theferromagnetic metal, magnetization becomes nonequilibrium, andspin-polarized electrons can be generated (source: R. Fiederling, M.Keim, G. Reuscher, W. Ossau G. Schemidt, A. WAAG & L. W. Molenkamp,Nature 402, 787-790 (1999), “Injection and detection of a spin-polarizedcurrent in a light-emitting diode”).

Therefore, a higher spin polarization degree can be obtained byutilizing this dilute magnetic alloy as the spin arrayed layer 52 whichalso has a function as a spin conduction layer.

As a dilute magnetic material alloy, for example, (In, Mn)As, (Ga,Mn)As, (Cd, Mn)Te, (Zn, Mn)Te, and (Zn, Cr)Te can be cited.

It is enough that a position of the spin arrayed layer 52 including thedilute magnetic alloy is between two ferromagnetic layers (ferromagneticfixed layer 23 and ferromagnetic free layer 25). However, the positionof the spin arrayed layer 52 including the dilute magnetic alloy is morepreferably between the reference, the ferromagnetic fixed layer 23 andthe spin conduction layer (spin conduction layer 24), and thereby apolarity degree of conduction spin in spin injection can be improved.

When the dilute magnetic alloy is included in the fullerene contained inthe spin conduction layer 24, the spin conduction layer 24 functions asthe spin arrayed layer and the spin conduction layer.

Further, it is possible that in order to run other circuit to performlogical operation according to reading results of recording information,for example, an amplification circuit of reading signals can beincorporated into the foregoing nonvolatile RAM. Further, though in theforegoing embodiment, the electrode layer 22, the ferromagnetic fixedlayer 23, the spin conduction layer 24, the ferromagnetic free layer 25,and the electrode layer 26 are formed in this order over the substrate21, deposition order of the respective layers can be opposite to theforegoing order.

EXAMPLE

In this example, a nonvolatile RAM having the following construction wasfabricated. Here, constructions from the electrode layer 26 to thesubstrate 21 will be shown.

<Sample Structure>

Electrode layer: Au film (25 nm thick)

Ferromagnetic free layer: permalloy film made of Ni₈₁Fe₁₉ (1 nm thick,and having uniaxial anisotropy so that the c axis becomes parallel tomagnetization of the ferromagnetic fixed layer)

Paramagnetic layer: La@C₈₂ thin film (20 nm thick)

Ferromagnetic fixed layer: permalloy film made of Ni₈₁Fe₁₉ (4 nm thick,and having uniaxial anisotropy)

Electrode layer: Au film (500 nm thick)

Substrate: silicon substrate

Measurement results of the sample structure of this example will behereinafter shown.

<Calculated Values>

Polarization efficiency: to 90%

In-plane effective anisotropy magnetic field for ferromagnetic freelayer: Hu=+2Ku/Ms to 10 Oe

Spin number density: to 1.9×10¹⁵ cm²

Gilbert attenuation coefficient: 0.005

Critical value Jt: to 8×10³ A/cm²

Electric resistance: 16 mΩ

Noise voltage (10 Hz BW, 77 k): 0.2 nV

<Measurement Values>

Switching current density by experiment: to 2×10⁴ A/cm²

Switching time θ (0 to π): to 0.05 μsec

Peak power consumption in reading: to 0.1 pW

Reading current density: to 3×10⁴ A/cm²

Reading current pulse: to 5.0 μA, 1 Hz

CPP GMR 4% ΔR/R: to (800 μΩ/20 mΩ)

Average reading voltage: to 5 nV

Further, as a comparative example for this example, a nonvolatile RAMwas fabricated as in this example, except that an Au film being 20 nmthick was used for the paramagnetic layer. Measurement results of thiscomparative example will be hereinafter shown.

<Calculated Values>

Polarization efficiency: to 30%

In-plane effective anisotropy magnetic field for free layer: Hu=+2Ku/Msto 10 Oe

Spin number density: to 1.9×10¹⁵ cm²

Gilbert attenuation coefficient: 0.01

Critical value Jt: to 8×10³ A/cm²

Electric resistance: 16 mΩ

Noise voltage (10 Hz BW, 77 k): to 0.3 nV

<Measurement Values>

Switching current density by experiment: to 2×10⁴ A/cm²

Switching timeθ (0-π): to 0.1 μsec

Peak power consumption in reading: to 0.1 pW

Reading current density: to 4×10³ A/cm²

Reading current pulse: to 6.4 μA, 1 Hz

CPP GMR 4% ΔR/R: to (800 μΩ/16 mΩ)

Average reading voltage: to 5 nV

As evidenced by the foregoing, in this example, polarization efficiencycould be significantly improved by using the La@C₈₂ film for theparamagnetic layer instead of the Au film. That is, it was found thatwhen the La@C₈₂ film was used for the paramagnetic layer instead of theAu film, performance of the nonvolatile RAM could be improved.

Further, as a comparative example to this example, measurement resultsof the conventional induced magnetic field type memory element will behereinafter shown.

<Measurement Values>

Switching current density: to 5.8×10⁶ A/cm²

Switching timeθ (0 to π): to 0.08 μsec

Peak power consumption in reading: to 1.0 pW

Reading current density: to 1×10⁵ A/cm²

Reading current pulse: to 5.0 μA, 1 Hz

CPP GMR 4% ΔR/R: to (800 μΩ/20 mΩ)

Average reading voltage: to 40 nV

Compared to the conventional induced magnetic field type memory element,respective characteristics were improved as follows: the currentrequired for switching and writing was increased by two-digit order; theswitching time was increased by one-digit order; and the powerconsumption was increased by one-digit order. That is, it was found thatcompared to the conventional induced magnetic field type memory element,the spin injection type memory element could reduce reading time andpower consumption.

Next, another embodiment of the invention will be described.

Second Embodiment

FIG. 19 shows a construction of a memory element according to a secondembodiment of the invention. This memory element MM2 is also “spininjection type” wherein writing is performed by generating magnetizationinversion by injecting polarized spin electrons. A basic structurethereof is that a spin conduction layer 3 is provided between twoferromagnetic layers, that is, a fixed layer 1 wherein its magnetizationorientation is fixed to a certain direction, and a free layer 2 whereinits magnetization orientation is changed by injecting the polarized spinelectrons.

These respective layers are formed in layers inside a carbon nanotube 10of one molecule. That is, the carbon nanotube 10 constructs onecomposition unit of a memory by setting a central part in the axisdirection to the spin conduction layer 3, and including the fixed layer1 and the free layer 2 in the both ends thereof Further, the fixed layer1 and the free layer 2 are provided with electrode layers 4A and 4B,respectively. The individual magnetic memory element MM2 is connected towiring layers 5A and 5B through the electrode layers 4A and 4B.

The spin conduction layer 3 is constructed from part of the hollowcarbon nanotube 10. The spin conduction layer 3 is constructed from anonmagnetic material to shield magnetic interaction between the fixedlayer 1 and the free layer 2. Further, a spin coherence length of thespin conduction layer 3 should be longer than at least a layer thicknessitself, in order to conduct polarized spin electrons between the fixedlayer 1 and the free layer 2. Regarding the carbon nanotube, variousreports suggesting its ballistic conduction have been made. Recently, ithas been experimentally confirmed that its spin coherence length is 200nm or more (K. Tsukagoshi, B. W. Alphenaar and H. Ago, “Spin coherenttransport in a ferromagnetically contacted carbon nanotube,” Nature 401,572-574 (1999)). Meanwhile, a thickness of the spin conduction layer 3here (length of the carbon nanotube) is about from 0.5 nm to 5 μm as apractical range. Therefore, this spin conduction layer 3 concurrentlysatisfies the foregoing two conditions.

As described above, in this embodiment, (1) part of the carbon nanotube10 is utilized as the spin conduction layer 3, and (2) the carbonnanotube 10 constructs an outer hull of the whole element.

In Japanese Patent Publication No. 2546114, a technique to includevarious different substances in a hollow hole placed in a center of acarbon nanotube is disclosed. Regarding a carbon nanotube including amagnetic material, descriptions are given as follows: (1) since a tubeinternal diameter (5 to 10 nm) is smaller than a magnetic domain size ofa general magnetic material, such a carbon nanotube is considered as asimple magnetic domain particle, and (2) when the tubes are arranged sothat their long axes are placed vertically, a perpendicular magneticrecording medium having a very high density can be realized due to theanisotropy. However, in the foregoing Japanese Patent Publication No.2546114, there is no description on application of the carbon nanotubeto a memory.

The largest effects obtained from that the carbon nanotube 10 is used asan outer hull of the element is that it becomes possible to preventeffects of proximal magnetic fields to the inside thereof due tomagnetic shielding effects by its n electron cloud. The magnetic memoryelement MM2 of this embodiment is characterized by the current-driventype. However, if its size (cell size) becomes nano order, a leakagemagnetic field generated by a reading current may disturb magnetizationof proximal cells. However, since the carbon nanotube 10 covers themagnetic layers inside the element, and shields magnetic disturbancefrom the outside, magnetization directions of the fixed layer 1 and thefree layer 2 are always maintained stably. Thereby, the magnetic memoryelement MM2 becomes an element, which is fine sized, and can beintegrated and driven practically.

Further, an internal diameter of the carbon nanotube 10 is very little,which is about from 1 to 10 nm. That is, such a fine element can beformed without depending on the conventional semiconductor processingtechnology. At the same time, the size is considerably smaller than themagnetic domain size of the general magnetic material. Therefore, it isthinkable that the magnetic material has a simple magnetic domainstructure inside the carbon nanotube 10. In the result, since transportof the magnetic domain to magnetization is not associated, it isexpected that retentivity of the magnetic material becomes larger.

Examples of the ferromagnetic materials used for the fixed layer 1 andthe free layer 2 include simple substances of Fe and Co, binary alloysthereof, NiFe alloy, MnFeCo, and FeCoNi. Of the foregoing, theferromagnetic material effective to obtain a high polarity ratio ofelectrons is FeCo alloy having a high Fe content ratio. Itinerant delectrons of 3d ferromagnetic material have isotropic andfree-electron-wise wavenumber vectors. Therefore, it is not rathernecessary to consider crystal orientation. It is preferable that thefixed layer 1 is selected from a hard magnetic material containing Ni,Co and the like, and the free layer 2 is selected from a soft magneticmaterial such as pure iron and permalloy (Ni₇₉Fe₂₁). Further, metalnanoparticle materials such as spinel type ferrimagnetic particles whosemain component is iron oxide containing cobalt nickel, whose highretentivity has recently become known (crystal particle diameter: φ to30 nm, coercivity: HcJ to 6 k Oe), and FeO₂ particles (firingtemperature: 1023 K, crystal particle diameter: φ to 5 nm, HcJ to 1 kOe) can be used.

For the fixed layer 1, in order to maintain the constant magnetizationorientation, it is preferable that a material whose gilbert attenuationcoefficient is significantly larger than of the free layer 2 is used, oruniaxial anisotropy larger than of the free layer 2 is applied byadjusting its composition and its layer thickness (thicker than of thefree layer 2). Otherwise, it is possible that an anti-ferromagneticlayer is contacted to the fixed layer 1 to pin the magnetization. Whenthe anti-ferromagnetic layer is made of a metal, the anti-ferromagneticlayer also has a function as the electrode layer 4A. Examples of such aanti-ferromagnetic metal material include FeMn, IrMn, NiMn, and RhMn.

Meanwhile, it is preferable that the free layer 2 is provided withuniaxial anisotropy of anisotropic magnetic field Hu>100 Oe byoptimizing its composition, thickness, cross section area (diameter ofthe carbon nanotube 10) and the like in order to prevent fluctuation ofthe magnetization direction (memory state) due to influence of heat ormagnetic fields. The magnetization direction of the free layer 2 can bechanged in the in-plane two directions, or can be changed in thein-plane direction and the direction perpendicular to the plane. In thelatter case, it is preferable that a thickness of the free layer 2 is 5atomic layers or less, that is, about 1 nm, in order to obtainsufficient perpendicular magnetic anisotropy.

Any type of the electrode layers 4A and 4B can be used, as long as theelectrode layers 4A and 4B are made of paramagnetic metals havingconductivity. A thickness and a shape thereof are not particularlylimited. This magnetic memory element MM2 is included in the hull of thecarbon nanotube. Dimensions of the magnetic memory element MM2 aresmaller than of the general memory element, and a ratio of its thicknessis higher than of its cross section. Therefore, the electrode layers 4A,4B and the wiring layers 5A, 5B can be formed by using the conventionalsemiconductor processing technology, or can be constructed from amolecule wire such as the carbon nanotube.

In this magnetic memory device MM2, as described later, both writing andreading are performed by applying a current. Therefore, wirings forwriting and reading can be shared, and it is enough to use two wiringlayers 5A and 5B. Such simplicity of the wiring structure is one of theadvantages thereof.

Further, in the magnetic memory element MM2, the carbon nanotube 10 isused as an outer hull of the element. Therefore, the magnetic memoryelement MM2 is also characterized by integration. In general, the carbonnanotubes easily form a conglomeration body called a bundle. The outerhull of the magnetic memory element MM2 is constructed from the carbonnanotube 10. Therefore, integration is easily made by conglomeration.For example, as shown in FIG. 20, when the magnetic memory elements MM2are arranged in a state of a matrix, this regular arrangement ismaintained by dispersion force (force for conglomeratizing the carbonnanotube 10), and a memory body of a magnetic memory device isconstructed from the integrated magnetic memory elements MM2. Thereby,the memory device having a high density and high reliability whose unitmemory cell is one carbon nanotube can be fabricated.

Such a magnetic memory element MM2 and its magnetic memory device can bemanufactured by, for example, producing an oriented carbon nanotube byusing oriented carbon nanotube production method (Jeong et al., Chem.Mater., Vol 14, No. 4, pp 1859-1862 (2002)), filling a magnetic metal ina hollow part of the tube, and performing electric joint at end parts.Specific descriptions of this method will be given later as an example.

Next, an operation method thereof will be hereinafter described. In themagnetic memory element MM2, information is recorded by making a statewherein a magnetization direction of the free layer 2 to the fixed layer1 is parallel magnetization alignment and a state wherein amagnetization direction of the free layer 2 to the fixed layer 1 isanti-parallel magnetization alignment correspond to binary data such as“0” and “1.” Data is written by inverting the magnetization direction ofthe free layer 2 by a pulse current applied in the directionperpendicular to the layer face (CPP: Current Perpendicular to Plane).For example, when magnetization of the free layer 2 to the fixed layer 1is changed from the parallel magnetization alignment to theanti-parallel magnetization alignment, a current density pulse isapplied from the fixed layer 1 to the free layer 2, and spin polarizedelectrons are injected from the free layer 2 to the fixed layer 1. Then,a magnitude of the current needs to be larger than the critical currentdensity value with which magnetic inversion is generated in the freelayer 2. During this pulse application, the magnetization direction ofthe free layer 2 is inverted, and the state of parallel magnetizationalignment of the free layer 2 and the fixed layer 1 is changed to thestate of anti-parallel magnetization alignment thereof.

On the contrary, when the state of anti-parallel magnetization alignmentis changed to the state of parallel magnetization alignment, current isapplied in the opposite direction. That is, a current is applied fromthe free layer 2 to the fixed layer 1, and the spin-polarized electronsare injected from the fixed layer 1 to the free layer 2.

Here, since the spin conduction layer 3 is constructed from the carbonnanotube, polarized electrons are conducted through the layer withoutspin relaxation. Therefore, electrons are injected into the fixed layer1 and the free layer 2 in a state that their spin angular momentum ismaintained, and reading can be performed effectively.

Reading data, that is, identifying the foregoing two magnetizationstates can be performed by using, for example, giant magnetoresistiveeffects in the direction perpendicular to the layer face (CPP-GMR: GiantMgneto-Resistive). In addition, there is a method using magnetic Kerreffect.

As described above, in the spin injection type magnetic memory elementMM2 in this embodiment, two ferromagnetic layers, that is, the fixedlayer 1 and the free layer 2 are filled respectively in the both ends ofthe one molecule carbon nanotube 10, and the hollow part itself in thecenter is set to the spin conduction layer 3. Therefore, the spinconduction layer 3 has good spin coherence of the carbon nanotube. Thepolarized electrons are injected into the fixed layer 1 and the freelayer 2 without spin relaxation. Therefore, writing can be performedeffectively, and low-power-consumption driving is enabled.

Further, the main body of the memory element is housed inside the hullof the carbon nanotube 10. Therefore, the nano-sized element can berealized without depending on the conventional microfabricationtechnology. Therefore, it is possible to obtain a very high densitymemory device by using this magnetic memory element MM2. In this case,it is thinkable that the fixed layer 1 and the free layer 2 have thesingle magnetic domain structure, and stable magnetization orientationscan be maintained. Further, the magnetization orientations can be alwaysstably maintained also by the fact that the Xelectron cloud of thecarbon nanotube 10 covers the fixed layer 1 and the free layer 2, andshields magnetic disturbance from the outside. Further, the carbonnanotube 10 has the one dimensional shape and dispersion force worksbetween the tubes. Therefore, conglomeration is realized in the axisdirection. Consequently, the magnetic memory element MM2 can be highlyoriented stably and easily, and the highly integrated magnetic memorydevice can be obtained.

Further, a higher spin polarization degree can be obtained by providinga spin arrayed layer 11 including a dilute magnetic alloy as in thefirst embodiment, as shown in FIG. 21 in addition to the foregoing spinconduction layer 3. It is enough that a position of the spin arrayedlayer 11 is between two ferromagnetic layers (ferromagnetic fixed layer1 and ferromagnetic free layer 2). However, the position is morepreferably between the reference ferromagnetic fixed layer 1 and thespin conduction layer 3. Thereby, a polarization degree of theconduction spin in spin injection can be improved.

Further, a specific example of the invention will be hereinafterdescribed in detail.

EXAMPLE 1

First, a high purity aluminum sheet (99.999%) was degreased by acetone,and washed with ethanol solution. The resultant was electropolished in amixed solution of perchloric acid and ethanol. Subsequently, theresultant was anodized at 40 V in 0.3 M of oxalic acid at 15° C. for 12hours. Thereby, an anodized alumina substrate with fine pores wasobtained. These fine pores were self-assembled as a nano-size orderedporous structure, and form an ordered array over a long distance. Thepractically obtained fine pore passed through the alumina substrate(that is, the fine pore was in a state that its both ends were opened),and its diameter was 80 nm and its density was 1.0×10¹⁰ pores/cm².

Next, the alumina substrate was precipitated in CoSo₄.7H₂O solution, andapplied with 18 V AC for 1 minute. Thereby, Co catalyst waselectrochemically precipitated on a bottom part of the fine pores of thesubstrate. Co particles on the surface were deoxidized by exposing thesubstrate to a mixed gas of 10% of H₂ and 90% of Ar at 500° C. for 1hour. This Co catalyst was a catalyst for producing the carbon nanotube,and would become the magnetic layer (fixed layer) of the magnetic memoryelement.

Next, 10% of C₂H₂ and 20% of H₂ were contained in Ar carrier gas, whichwas provided to the foregoing resultant to grow the carbon nanotubes inthe fine pores of the substrate by thermal decomposition method.

Extra grown portions of the carbon nanotubes were cut by providingultrasonic treatment with 40 kHz in acetone solution for the wholesubstrate. Thereby, nanotubes having the same length oriented in theaxis direction were obtained.

Next, the whole substrate with the carbon nanotubes was soaked in anacid bath containing iron ions and hypophosphite as a reducing agent,and pure iron was filled in the carbon nanotubes until metallic colorwas shown by using electroless plating method. Thereby, the individualcarbon nanotube obtained a basic structure of the spin injection typemagnetic memory element. That is, a Co layer of a hard magnetic materialas the fixed layer, a hollow nanotube as the spin conduction layer 3,and a Fe layer as the free layer are formed. As an electrode and anextraction wiring, nanotubes with a thinner diameter were jointed atboth ends of this nanotube including magnetic material by atommanipulation method.

Further, the whole alumina substrate of these nanotubes was laid on aninsulative substrate made of SiO₂, and soaked in 0.1 M of NaOH at 70° C.for 3 hours, and thereby the alumina substrate was decomposed andremoved. Then, a bundle structure constructed from the nanotubesincluding magnetic material and tubes to become electrodes and wiringsremained on the insulative substrate.

Next, a signal wiring was bonded to the extraction wiring, which wasused as a two dimensional lattice wiring to obtain the address. Finally,the insulative substrate was firmly fixed to a Cu heat sink. Themagnetic memory device was thereby completed.

Further, characteristics of the fabricated magnetic memory device weremeasured. The results will be hereinafter shown.

<Calculated Values>

Polarization efficiency: to 50%

In-plane effective anisotropy magnetic field for free layer: Hu=+2Ku/Msto 100 Oe

Spin number density: to 5.0×10¹⁵ cm²

Gilbert attenuation coefficient: 0.01

Critical value Jt: to 8×10³ A/cm²

Electric resistance: 16 mΩ

Noise voltage (10 Hz BW, 77 k): 0.2 nV

<Measurement Values>

Switching current density by experiment: to 1×10⁴ A/cm²

Switching timeθ (0-π): to 0.05 μsec

Peak power consumption in reading: to 0.1 pW

Reading current density: to 3×10³ A/cm²

Reading current pulse: to 6.4 μA, 1 Hz

CPP-GMR 4% ΔR/R: to (800 μΩ/16 mΩ)

Average reading voltage: to 5 nV

Magnetic recording density: to 6.5 Gbit/inch²

The measured recording density can be improved by controlling the finepore diameter of the anodized alumina substrate, and optimizing thenanotube diameter, that is, the diameter of the magnetic memory element.It is possible to control the fine pore diameter in the range fromseveral 10 to several 100 nm by controlling a starting point of the finepore growth by, for example, ion sputtering method with Ar, Ga and thelike to the electropolished aluminum substrate.

EXAMPLE 2

The carbon nanotube including the ferromagnetic metal can be obtained bymaking a graphite electrode used in synthesis by arc discharge methodand the like contain the ferromagnetic metal. In this example, themagnetic memory device was assembled by the carbon nanotube obtained asabove.

First, a mixture in which Ni, Y, and permalloy (NiFe alloy) powders wereadded at a weight ratio of 4%, 1%, and 4% to graphite powders wasfabricated. Further, carbon pitch was added to the mixture, which wasfired at 900° C. for 6 hours. Arc discharge by contact arc method wasperformed in He atmosphere and 200 Torr by using the resultant as acathode electrode.

Obtained carbon shoot was dispersed in the magnetic field, and thereby ananotube including magnetic material was selectively taken out. Since Niworks as a catalyst for producing the carbon nanotube, Ni is included inan end of almost all tubes. Therefore, tubes in which the permalloy isfilled in other end need to taken out selectively. Next, of the obtainedmagnetic nanotubes, only the tubes in which the ferromagnetic Ni isincluded one end and the permalloy is included in other end werecollected by visually checking with a scanning electron microscope.

Each of these collected carbon nanotubes has a basic structure as thespin injection type magnetic memory element. That is, an Ni layer of ahard magnetic material as the fixed layer, a hollow nanotube as the spinconduction layer, and a permalloy layer as the free layer were formed.These carbon nanotubes are conglomeratized by Van der Waals' forces atintervals of about 0.3 nm from each other.

As an electrode and a lead wiring, nanotubes with a thinner diameterwere jointed at both ends of this nanotube including magnetic materialby atom manipulation method. After that, a magnetic memory device wascompleted by using subsequent steps similar to Example 1.

The invention is not limited to the foregoing embodiments and examples,and various modifications may be made. For example, in the secondembodiment, the part of the spin conduction layer 3 of the carbonnanotube 10 was used as a hollow part. However, it is possible tocontain a conductive paramagnetic material having a long spin coherencelength. Examples thereof include carbon materials such as fullerene, 3dmetals other than anti-ferromagnetic metal such as Ag and Au, and 4dmetals.

In the second embodiment, the magnetic memory element wherein the mainpart is formed in the carbon nanotube 10 has been described. However, itis possible that the carbon nanotube 10 is substituted with othercylindrical molecule such as a boron nitride (BN) tube and a peptidenanotube. In this case, it is possible to improve characteristics byfilling the foregoing carbon material or metal in the part correspondingto the spin conduction layer 3.

Further, in the second embodiment, the carbon nanotube 10 includes thefixed layer 1 and the free layer 2. It is possible that the carbonnanotube 10 includes part of the electrode layers 4A and 4B in order toimprove bonding characteristics. It is enough that in the magneticmemory element in the invention, at least the spin conduction layerprovided between the fixed layer and the free layer is constructed fromthe cylindrical molecule as typified by the carbon nanotube. It isoptional whether other components for the element are included or not.However, as mentioned above, it is expected that the conductivecylindrical molecule could give magnetic shielding effects, andtherefore, the inclusive structure is preferably selected according toneed.

According to the memory element or the memory device of the invention,the spin conduction layer is constructed from the spherical shell orcylindrical molecule material having a hollow. Therefore, it becomeseasy to control the spin coherence length, and the sufficient spincoherence length and a uniform spin field can be obtained. Therefore, itbecomes possible to prevent scattering of the spin-polarized conductionelectrons in the paramagnetic layer, to improve reliability, and therebyto attain practical use thereof Further, compared to the conventionalinduced magnetic field method, the upper limit of the recording densitycan be significantly improved, and reading time and power consumptioncan be reduced. In particular, the uniform thin film can be grown byforming the spin conduction layer from the spherical shell moleculematerial including the paramagnetic material.

Further, the spin conduction layer is constructed from the cylindricalmolecule, and the central part in the axis direction of this cylindricalmolecule functions as the spin conduction layer. In addition, the firstferromagnetic layer is included in one end of this cylindrical molecule,and the second ferromagnetic layer is included in the other end thereof.Thereby, construction wherein the element body is housed in the hollowpart of the cylindrical molecule is obtained. Therefore, the nano-sizedspin injection type memory element can be realized without depending onthe conventional microfabrication technology by selecting the nano-sizedcylindrical molecule. That is, despite of its fine size, the elementwhose dimensions are well controlled can be obtained by the simplemanufacturing method. In this case, it is thinkable that the first andthe second ferromagnetic layers have simple magnetic domain structuredue to the diameter size of the cylindrical molecule. Further, sincethese layers are included in the cylindrical molecule, magneticdisturbance from the outside is shielded. Therefore, the magnetizationdirection can be stably maintained. Due to the magnetic shieldingeffects, integration becomes practically enabled despite of its finesize.

Further, by using the carbon nanotube as the cylindrical molecule, inthe spin conduction layer, polarized electrons are conducted whilealmost no spin is relaxed due to good spin coherence of the carbonnanotube, and the polarized electrons are injected into the firstferromagnetic layer or the second ferromagnetic layer. Therefore, it ispossible to realize the nano-sized spin injection type memory elementhaving good writing efficiency.

Further, according to the memory device of the invention, the pluralityof memory elements of the invention are arrayed. Therefore, writing canbe performed effectively, and low-power-consumption drive is enabled. Inparticular, when the individual memory element is constructed by usingthe cylindrical molecule, the cylindrical three dimensional structurecan be obtained differently from the element which is two dimensionallyformed by the conventional thin film fabrication technology. Therefore,the memory elements can be integrated in the vertical direction.Further, this memory element is the spin injection type memory element,and hardly receive influence of adjacent magnetic fields compared toother magnetic memories. Therefore, a distance between memory cells canbe further narrowed, and high density integration becomes enabled.

1. A memory element wherein recording information is written byinjecting spin-polarized electrons comprising: a spin conduction layermade of a spherical shell or cylindrical molecule material having ahollow, and wherein the spin-polarized electrons are conducted by thespin conduction layer.
 2. A memory element according to claim 1comprising: a first ferromagnetic layer wherein a magnetizationdirection is fixed; a spin conduction layer made of a spherical shellmolecule material having a hollow in which a paramagnetic material isincluded and having a given spin coherence length, which is formed overthe first ferromagnetic layer; and a second ferromagnetic layer formedon the spin conduction layer on the side opposite to the firstferromagnetic layer, wherein a magnetization direction is changed by thespin-polarized electrons, wherein the recording information is writtenby changing the magnetization direction of the second ferromagneticlayer.
 3. A memory element according to claim 2, wherein the sphericalshell material constructing the spin conduction layer is carbon moleculefullerene.
 4. A memory element according to claim 3, wherein thespherical shell molecule material is carbon molecule fullerene having ahollow sized from 0.1 nm to 50 nm.
 5. A memory element according toclaim 2, wherein a thickness of the spin conduction layer is from 0.5 nmto 5 μm.
 6. A memory element according to claim 2, wherein theparamagnetic material included in the spherical shell molecule materialis lanthanum (La), cesium (Cs), dysprosium (Dy), europium (Eu), orgadolinium (Gd).
 7. A memory element according to claim 2, wherein theparamagnetic material included in the spherical shell molecule materialis nitrogen (N) or phosphorous (P).
 8. A memory element according toclaim 2 comprising a spin arrayed layer between the first ferromagneticlayer and a second ferromagnetic layer.
 9. A memory element according toclaim 8, wherein the spin arrayed layer includes a dilute magneticmaterial.
 10. A memory element according to claim 9, wherein the dilutemagnetic material is made of at least one of (In, Mn)As, (Ga, Mn)As,(Cd, Mn)Te, (Zn, Mn)Te, and (Zn, Cr)Te.
 11. A memory element accordingto claim 2, wherein the spherical shell molecule material includes adilute magnetic material, and the spin conduction layer also functionsas a spin arrayed layer.
 12. A memory element according to claim 2,wherein a thickness of the first ferromagnetic layer is thicker than athickness of the second ferromagnetic layer.
 13. A memory elementaccording to claim 2 comprising a magnetization fixed layer for fixingthe magnetization direction of the first ferromagnetic layer on theopposite side of the first ferromagnetic layer to the spin conductionlayer.
 14. A memory element according to claim 13, wherein themagnetization fixed layer is made of an anti-ferromagnetic material. 15.A memory element according to claim 13, wherein the magnetization fixedlayer also functions as an electrode.
 16. A memory element according toclaim 2, wherein a thickness of the second ferromagnetic layer is 5atomic layers or less.
 17. A memory element according to claim 2,wherein electrodes are formed at both faces respectively, and theelectrodes are made of a paramagnetic metal material.
 18. A memoryelement according to claim 1, wherein a writing line for injecting thespin-polarized electrons is connected to the second ferromagnetic layer.19. A memory element according to claim 2, wherein a cell area is from0.5 nm² to 5 μm².
 20. A memory element according to claim 2, wherein therecording information is read by utilizing giant magnetoresistiveeffects generated in applying a current.
 21. A memory element accordingto claim 2, wherein the recording information is read by illuminatingthe second ferromagnetic layer with light, and utilizing magnetic Kerreffect then generated.
 22. A memory element according to claim 1comprising: first and second ferromagnetic layers wherein amagnetization direction change of at least one thereof is induced byinjecting spin-polarized electrons; and a spin conduction layerconstructed from at least part of a hollow cylindrical molecule arrangedby setting its axis direction to a laminating direction of the first andthe second ferromagnetic layers, which is provided between the firstferromagnetic layer and the second ferromagnetic layer to shieldmagnetic interaction thereof and which conducts the spin-polarizedelectrons.
 23. A memory element according to claim 22, wherein a centralpart in the axis direction of the cylindrical molecule functions as thespin conduction layer, and the first ferromagnetic layer and the secondferromagnetic layer are included in one end and the other end,respectively.
 24. A memory element according to claim 22, wherein amolecule of the cylindrical molecule is a composition unit of theelement.
 25. A memory element according to claim 22, wherein the spinconduction layer made of the cylindrical molecule has a length in itsaxis direction which is shorter than its spin coherence length atoperation temperatures.
 26. A memory element according to claim 22,wherein the spin conduction layer made of the cylindrical moleculeincludes other molecule or atom in a hollow part.
 27. A memory elementaccording to claim 22 comprising a spin arrayed layer between the firstferromagnetic layer and the second ferromagnetic layer.
 28. A memoryelement according to claim 27, wherein the spin arrayed layer includes adilute magnetic material.
 29. A memory element according to claim 28,wherein the dilute magnetic material is made of at least one of (In,Mn)As, (Ga, Mn)As, (Cd, Mn)Te, (Zn, Mn)Te, and (Zn, Cr)Te.
 30. A memoryelement according to claim 26, wherein a spin coherence length of themolecule or the atom included in the hollow part at operationtemperatures is longer than the length of the spin conduction layer inthe axis direction of the cylindrical molecule.
 31. A memory elementaccording to claim 22, wherein the cylindrical molecule is a carbonnanotube.
 32. A memory device constructed from an arrayed plurality ofmemory elements, wherein the memory element comprises a spin conductionlayer made of a spherical shell or cylindrical molecule material havinga hollow, and spin-polarized electrons are conducted by the spinconduction layer.
 33. A memory device according to claim 32, wherein thememory element comprises: a first ferromagnetic layer wherein amagnetization direction is fixed; a spin conduction layer made of aspherical shell molecule material having a hollow in which aparamagnetic material is included and having a given spin coherencelength, which is formed over the first ferromagnetic layer; and a secondferromagnetic layer formed on the spin conduction layer on the sideopposite to the first ferromagnetic layer, wherein a magnetizationdirection is changed by the spin-polarized electrons, wherein recordinginformation is written by changing the magnetization direction of thesecond ferromagnetic layer.
 34. A memory device according to claim 33,wherein the spherical shell molecule material constructing the spinconduction layer is carbon molecule fullerene.
 35. A memory deviceaccording to claim 32, wherein the memory element comprises: first andsecond ferromagnetic layers wherein a magnetization direction change ofat least one thereof is induced by injecting the spin-polarizedelectrons; and a spin conduction layer constructed from at least part ofa hollow cylindrical molecule arranged by setting its axis direction toa laminating direction of the first and the second ferromagnetic layers,which is provided between the first ferromagnetic layer and the secondferromagnetic layer to shield magnetic interaction thereof and whichconducts the spin-polarized electrons.
 36. A memory device according toclaim 35, wherein the memory elements are integrated by being arrayed byaligning the axis directions of the cylindrical molecules.